axial projection

; axial view radiographic projection to visualize sesamoid bones within the tendon of extensor hallucis brevis at the plantar aspect of the first metatarsophalangeal joint, with the foot placed in a position simulating toe off (seeTable 1)

Table 1: Common radiographic projections of the foot and ankle

Projection

Visualization

Foot projections

Dorsiplantar (DP) projection or anteroposterior (AP) view

Weight-bearing with the beam directed at 15° to the frontal plane, to eliminate distortion due to the angulation of the metatarsals and centred on the metatarsal shaftsIt is used to visualize the phalanges, metatarsophalangeal joints, the metatarsals and the midfoot

Lateromedial oblique projection

Weight-bearing with the beam angled at 45° to the lateral side of the sagittal plane and centred on the forefoot; or non-weight-bearing, with the beam vertical and foot everted so that the plantar surface is at 45° to the ground surfaceIt is used to visualize the phalanges, metatarsals, metatarsocuneiform joints and sesamoids, but tends to give an elongated image of bony architecture

Mediolateral oblique projection

Weight-bearing with the beam angled between 25 and 45° to the medial side of the sagittal plane and centred on the forefootIt is used to visualize the first ray and associated structures, but tends to give an elongated image of bony architecture

Lateral projection

Weight-bearing or non-weight-bearing, with the beam angled at 90° to the lateral aspect of the foot and centred on the mid- or hindfootIt is used to visualize the profile of the whole foot, but obscures the midtarsal joint, due to superimposition of local structures

Digital projection

The lateromedial oblique projection is useful to visualize subungual exostoses, especially when the hallux (or affected toe) is raised up on a pad

Sesamoid projection or skyline projection

Weight-bearing, with the metatarsophalangeal joints dorsiflexed to 45° and the beam angled to be parallel to the ground surface on the sagittal plane, and centred on the plantar aspect of the forefootIt is used to visualize the relationship of the sesamoids with the head of the first metatarsal

Tarsal and ankle projections

Anteroposterior view

Weight-bearing with the beam angled at 90° to the frontal plane and the beam centred on the ankle jointUsed to visualize the ankle mortise and the trochlear surface of the talus

Axial calcaneal projection

Weight-bearing with the beam angled at 45° to the posterior aspect of the sagittal plane with the beam centred on the hindfootIt is used to visualize calcaneal trauma

Harris-Beath projection

Similar to the axial calcaneal projection, but the patient is positioned as if making a ski-jump, that is, weight-bearing with the foot dorsiflexed at the ankle and the beam angled at 45° to the posterior aspect of the sagittal plane with the beam centred on the ankleIt is used to visualize the subtalar joint where talar fusions are suspected

Radial, axial and tangential projections of the contact zone between the roller and work are made, then the radial projection area Sr, axial projection area Sz and tangential projection area St can be obtained, as shown in the Figure 3 ~ 5.

As shown in the Figure 4, the axial projection area can be expressed as Sz = arcsin [b/Rs] R[s.

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